This invention relates to powder metallurgy, and more particularly to ferroalloys dispersed and hot compacted into a metal matrix powder.
A known method of increasing the resistance of metallic materials to scoring wear is the insertion of hard particles (HP) which offer resistance to scoring caused by abrasive particles (AP). The efficiency of HP will be optimal when they are (a) harder than the attacking AP,(b) larger than the score cross-section, (c) dispersed in the metal matrix (MM), and (d) fixedly bonded to the metal matrix.
With regard to (a): materials appearing as AP are e.g. natural minerals; most of these natural minerals have a hardness of  less than 1000 V.P.N. (Vickers penetration hardness number), whereas quartz having a hardness of xcx9c1200 V.P.N. and corundum having a hardness of xcx9c2000 V.P.N. are much harder. The hardness of synthetic abrasives is sometimes even higher than that. The HP should have a hardness of from 2000 to 3000 V.P.N. to prevent them being scored especially by harder AP.
With regard to (b): the score widths occurring after erosion are frequently widths of a few xcexcm, whereas the score widths after grain slip wear and scoring wear are often widths of a few 10 xcexcm. Hence, HP are required, which have a mean size between 30 and 130 xcexcm; these values are to be understood as mean diameter or as mesh number.
With regard to c: a dispersion of the HP means that they are arranged in the MM at a mean distance from one another and are therefore not in contact with one another. This results in the shortest mean score length in the matrix and in the highest fracture toughness of the composite material. The adjustment of a dispersion is not trivial and depends on the volume and diameter ratios of the HP and MM powders.
With regard to (d): the bond between HP and MM is established by interdiffusion during hot compacting. Normally, it will be firmer for HP consisting of metal/metalloid compounds than e.g. for metal oxides. The materials used as metalloids are B, C and N, whereas the materials used as metals are some of the subgroups of the 4th to 6th periods, titanium being of particular interest in view of its availability and in view of the high stability and hardness of its metalloid compounds.
The demands (a) to (d) can, in total, only be fulfilled with a metal matrix particle composite material. In the prior art, it is known to mix carbide, boride or nitride powder with a metal matrix powder, the mixing being followed by a hot-compacting step. The formation of titanium boride, carbide and carbonitride from titanium powder and boron or carbon black, if desired, under nitrogen, takes place exothermically until melting occurs. This reaction has already been utilized for producing in situ a composite material from titanium particles mixed with metalloid and MM powder by means of high-temperature synthesis. Instead of titanium powder, also ferrotitanium powder has been used; in this case, the local melting (fusion) led to fine, xcexcm-sized precipitations due to the in-situ formation of TiC.